The present invention relates to vision inspection systems and processes which determine interrelationships between dimensions of parts to be inspected.
Mechanical tolerance testing of parts (for example, testing of threaded members by ring gauges, taper gauges, lead gauges, thread gauges, rulers and scales) have been used for years. Slip gauges and other apperati (for example, the AccuThread.RTM. gauge by Coulter Services, Inc; Actis.RTM. by TuboScope, Inc; MRP.RTM. gauges by gagemaker, Inc.) have also been used. Finally, visual inspection systems have recently been used for inspection of parts such as bolts coming off of assembly lines, as described in U.S. Pat. No. 4,581,762, incorporated by reference.
A common failing of all of the above mechanical measurement processes and devices is the inability to measure a wide variety of differently sized parts. For example, for each threaded size pipe to be measured, a different size gauge must be on hand to measure the various parameters required (examples of the parameters to be measured include pitch diameter, ovality, lead, taper, thread height, and L4 (the distance from the end of the pen to the last visible thread). Visual inspection systems have been limited by the resolution of the imaging techniques applied. For example, a wide angle lens, (which is capable of including a large device in its field of view) has less resolution than a more narrow angle lens, when both are set at the same distance from the object to the image. Increased fields of view can be accomplished by backing up narrow angle lens, but again, resolution is compromised.
Accordingly, there is a need for a measurement process system which is accurate over a wide variety of sizes and shapes of parts. There is also a need for the resolution achieved in visual inspection systems using narrow angle cameras in inspection of large parts (for example, oil field pipe threads).